Phantom and method for producing same

ABSTRACT

The present invention relates to the phantom comprises water, an oil, an emulsifier and a water coagulating agent, and having a scattering coefficient of 5 to 20 cm−1 at a wavelength of 750 to 1000 nm.

TECHNICAL FIELD

The present invention relates to a phantom and a method for producing the phantom.

BACKGROUND

Near infrared spectroscopy (NIRS) covering a wavelength range of 650 to 1000 nm is widely used for noninvasively acquiring information of light absorption by hemoglobin, water and lipid in human tissues. NIRS is used as, for example, a method for monitoring tumor response in neoadjuvant chemotherapy for breast cancer. In application of NIRS, accurate measurement of the amounts of water and lipid in addition to the hemoglobin concentration is important. The hemoglobin concentration and the amounts of water and lipid reflect, for example, angiogenic activity, anti-inflammatory response and edema volume, and can serve as prognostic biomarkers in chemotherapy. Phantoms in which the amounts of water and lipid can be each controlled to fall within a predetermined range are useful for evaluating accuracy in measurement of the amounts of water and lipid in NIRS systems.

A variety of phantoms including water and lipid at various ratios have been heretofore proposed. For example, in Non Patent Literature 1, liquid phantoms are made by emulsifying different amounts of water and lipid, and instrumentally evaluated. Non Patent Literature 2 discloses a solid phantom made by incorporating a thickener rather than emulsifying water and an oil. Further, Patent Literature 1 discloses a specific oil-in-water emulsion to fill mannequins or phantoms used for measurement of specific absorption rate, measurement of total radiation power or measurement of total radiated sensitivity, the predetermined oil-in-water emulsion including an aqueous phase and an oil phase. Patent Literature 2 discloses a human body equivalent phantom formed by mixing purified water, a vegetable oil and detergent while adjusting electric properties by the mixing ratio of the purified water, the vegetable oil and the detergent, and forming the resulting mixture into a gel using kanten (agar-agar) and a thickener.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 6140720 -   Patent Literature 2: Japanese Unexamined Patent Publication No.     2008-119286

Non Patent Literature

-   Non Patent Literature 1: Merritt et. al., Technol Cancer Res Treat.,     2003, 2(6), 563-569 -   Non Patent Literature 2: Michaelsen et al., 2014, Journal of     Biomedical Optics, 2014, 19(2), 026012

SUMMARY

It is desirable that phantoms used for optical measurement by NIRS or the like have a scattering coefficient close to that of a living organism.

The present invention has been made in view of the above-described circumstances, and a problem to be solved by the present invention is to provide a phantom having a scattering coefficient close to that of a living organism.

The present invention relates to a phantom comprising water, an oil, an emulsifier and a water coagulating agent, and having a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm. The phantom of the present invention, which has the configuration described above, has a scattering coefficient close to that of a living organism. The water coagulating agent may be kanten (agar-agar).

The present invention relates to a method for producing a phantom, comprising a mixing step of mixing water, an oil, an emulsifier and a water coagulating agent to obtain a mixed liquid, the phantom having a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm.

It is preferable that the mixing step comprise producing an oil-in-water emulsion by performing stirring under a condition in which at least a part of the water, the oil and the emulsifier are present.

The method for producing a phantom according to the present invention may comprise a step of solidifying the mixed liquid.

According to the present invention, it is possible to provide a phantom having a scattering coefficient close to that of a living organism. The phantom of the present invention is also excellent in long-term stability of optical properties (absorption coefficient and scattering coefficient).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows microscope photographs showing the results of observing an oil-in-water emulsion;

FIG. 1B shows microscope photographs showing the results of observing a water-in-oil emulsion;

FIG. 2A shows a six-wavelength time-resolved spectroscopy system apparatus;

FIG. 2B shows a block diagram of the configuration of the apparatus;

FIG. 3 shows photographs showing the upper surfaces and the cut sections of various phantoms;

FIG. 4 shows a graph showing the results of measuring the lipid amount distributions of phantoms;

FIG. 5A shows a graph showing the results of measuring the absorption coefficients of phantoms;

FIG. 5B shows a graph showing the results of measuring the scattering coefficients of phantoms;

FIG. 6A shows a graph showing the results of measuring the amounts of water in phantoms;

FIG. 6B shows a graph showing the results of measuring the amounts of lipid in phantoms;

FIG. 7A shows a graph showing the results of testing the long-term stability of the absorption coefficients of phantoms;

FIG. 7B shows a graph showing the results of testing the long-term stability of the scattering coefficients of phantoms; and

FIG. 7C shows a graph showing the results of testing the long-term stability of the water and lipid contents of phantoms.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[Phantom]

A phantom of this embodiment comprises water, an oil, an emulsifier and a water coagulating agent, and has a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm. The phantom of this embodiment can be used, for example, for optical measurement, electrical measurement, measurement of physical properties and the like. The phantom of this embodiment has a scattering coefficient close to that of a living organism, and therefore can be suitably used as a phantom for optical measurement. Further, the phantom of this embodiment is also excellent in long-term stability of optical properties (absorption coefficient and scattering coefficient).

The phantom of this embodiment is an emulsified product containing the above-described components, preferably an oil-in-water emulsified product (oil-in-water emulsion). The phantom of this embodiment may be liquid, solid or gelatinous. It is preferable that the phantom of this embodiment be solid at 15 to 45° C. (preferably 37° C.) (a solid phantom).

Examples of the water include distilled water, common water, purified water, sterilized purified water, water for injection and distilled water for injection.

Examples of the oil include a vegetable oil, an animal oil and a mineral oil. Examples of the vegetable oil include soybean oil, rapeseed oil, olive oil and coconut oil. Examples of the animal oil include lard, fish oil, squalane and beeswax. Examples of the mineral oil include paraffin, hydrogenated polyisobutene, liquid paraffin, gelatinized hydrocarbons (plastibase and the like) and petroleum jerry. The oils may be used singly or in combinations of two or more thereof.

The volume ratio of water to the oil (lipid) (water:lipid) in the phantom may be 99:1 to 1:99, and is preferably 99:1 to 40:60, more preferably 80:20 to 60:40.

Examples of the emulsifier include lecithin, enzymatically decomposed lecithin (for example SLP-WhiteLyso), polysorbate 20 and sorbitan monostearate. It is preferable that the emulsifier be an emulsifier having an Hlb close to the Hlb of the oil used. The lecithin may be egg yolk-derived lecithin (egg yolk lecithin) or soybean-derived lecithin (soybean lecithin). It is preferable that the emulsifier be lecithin).

The content of the emulsifier may be 0.5% by mass or more, 0.6% by mass or more, 0.7% by mass or more, 0.8% by mass or more, 0.9% by mass or more, or 1.0% by mass or more, and may be 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less or 1.5% by mass or less per 100% by mass of the oil.

The water coagulating agent is a substance capable of solidifying a liquid containing water. Examples of the water coagulating agent include kanten (agar-agar), guar gum, agar, pectin and gelatin. The water coagulating agent may be water-soluble. Here, being water-soluble means that the solubility in water at 25° C. is 1.0 g/100 mL or more. Kanten is made from polysaccharides extracted from seaweed such as tengusa (agar weed) and ogonori (Chinese moss). Agar is made from dietary fiber (carrageenan) extracted from seaweeds such as Gigartina tenella and Chondrus ocellatus, or polysaccharide (locust bean gum) extracted from legume seeds.

The content of the water coagulating agent may be 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more or 0.5% by mass or more, and may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.8% by mass or less, 0.7% by mass or less or 0.6% by mass or less based on the total amount of the phantom.

The scattering coefficient of the phantom of this embodiment at a wavelength of 750 to 1000 nm is 5 to 20 cm⁻¹. The lower limit of the scattering coefficient at a wavelength of 750 to 1000 nm may be 5 cm⁻¹ or more, 6 cm⁻¹ or more, 7 cm⁻¹ or more, 8 cm⁻¹ or more, 9 cm⁻¹ or more or 10 cm⁻¹ or more, and the upper limit of the scattering coefficient of the phantom of this embodiment at a wavelength of 750 to 1000 nm may be 20 cm⁻¹ or less, 19 cm⁻¹ or less, 18 cm⁻¹ or less, 17 cm⁻¹ or less, 16 cm⁻¹ or less, 15 cm⁻¹ or less, 14 cm⁻¹ or less, 13 cm⁻¹ or less, 12 cm⁻¹ or less or 11 cm⁻¹ or less.

The scattering coefficient of the phantom of this embodiment at a wavelength of 750 to 1000 nm is a reduced scattering coefficient as measured by the method disclosed in Examples described later.

The scattering coefficient at a wavelength of 700 to 1000 nm can be adjusted by the types and amounts of an oil and an emulsifier to be used, control of emulsification conditions (for example temperature during emulsification), and the like.

The phantom may contain components other than water, an oil, an emulsifier and a water coagulating agent (other components). Examples of the other components include preservatives and inks.

The phantom of this embodiment can be kept solid at 15 to 45° C., and therefore can be used, for example, as a layered product obtained by stacking a plurality of phantoms having different water/lipid ratios (volume ratios of water to oil).

[Method for Producing Phantom]

One example of a method for producing a phantom according to this embodiment will be described. The method for producing a phantom according to this embodiment is a method for producing a phantom, comprising a mixing step of mixing water, an oil, an emulsifier and a water coagulating agent to obtain a mixed liquid, the phantom having a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm. The scattering coefficient of the phantom at a wavelength of 750 to 1000 nm may be within the range described above.

It is preferable that the mixing step comprise producing an oil-in-water emulsion by performing stirring under a condition in which at least a part of water, an oil and an emulsifier are present. The stirring may be performed under a condition in which the water coagulating agent is present, or is not present in addition to at least a part of water, an oil and an emulsifier. The mixing step can be carried out by mixing at least a part of water, an oil and an emulsifier at a time, and then stirring the resulting mixture. The stirring can be performed by using a blender.

In the mixing step, for example, the mixture of water, an oil and an emulsifier may be mixed with the water coagulating agent, or an oil may be mixed with water and the water coagulating agent in the presence of the emulsifier.

The mixture of water, an oil and an emulsifier may be one in which an oil-in-water emulsion is produced (oil-in-water emulsified product). As the mixture including water, an oil and an emulsifier, a commercialized product may be used as it is. Examples of the commercialized product usable as the mixture including water, an oil and an emulsifier include Intralipos (registered trademark) Injection, Intralipid, Lipovenoes, and ClinOleic (see OPTICS EXPRESS, 2008, Vol. 16, No. 8, 5908-5925, Table 1). The water coagulating agent may be dissolved in water, and mixed together with water.

The water may be mixed with the oil (lipid) at a volume ratio (water:oil) of 1:99 to 99:1, and the volume ratio (water:oil) is preferably 99:1 to 40:60, more preferably 80:20 to 60:40.

It is preferable that the emulsifier be lecithin. In this case, it is possible to further easily produce a phantom having a scattering coefficient close to that of a living organism.

The method for producing a phantom according to this embodiment may comprise a solidification step of solidifying the mixed liquid after the mixing step. The solidification step can be carried out by, for example, leaving the mixed liquid to stand at 0 to 10° C., 2 to 8° C. or 3 to 6° C. The solidification step can be carried out by, for example, leaving the mixed liquid to stand in a refrigerator.

Further, the method for producing a phantom according to this embodiment may comprise a stirring step of stirring the mixed liquid at 0 to 10° C. after the mixing step and before the solidification step. The temperature in stirring may be 0° C. or higher, or higher than 0° C., and may be 10° C. or lower or 5° C. or lower. The stirring step can be carried out by, for example, stirring the mixed liquid in iced water. The stirring step may be terminated at the time when solidification of the mixed liquid starts.

[Kit for Making Phantom]

One embodiment of the present invention provides a kit for making a phantom (hereinafter, also referred to as “this kit”), the kit comprising water, an oil, an emulsifier and a water coagulating agent. The emulsifier and the water coagulating agent may be each mixed with water or an oil beforehand, or may be included independently in this kit. This kit may further comprise the above-described other components (preservative, ink and the like). The other components may be mixed with water, the oil, the emulsifier or the water coagulating agent beforehand, or may be included independently of these components in this kit.

EXAMPLES

Hereinafter, the present invention will be described more specifically based on Examples. However, the present invention is not limited to the following examples.

<Making Phantom>

Example 1

1200 mL of water was boiled, and 6 g of kanten (agar-agar) was dissolved in the boiled water (5 g per 1000 mL of water). 950 mL of the water having dissolved kanten was collected while being filtered through a screen, and was cooled to 60° C. 50 mL of Intralipos (registered trademark) Injection 20% (Otsuka Pharmaceutical Factory, Inc.) was dissolved in the water. The obtained mixed liquid was transferred into a container, and stirred with a glass rod while being cooled with iced water, and was put in a refrigerator at the time when the liquid started setting, so that the liquid was solidified. In this way, a phantom of Example 1 (water:lipid=99:1 (volume ratio)) was obtained. Intralipos (registered trademark) Injection 20% contains 10 g of purified soybean oil, 0.6 g of purified egg yolk lecithin, 1.1 g of concentrated glycerin and an appropriate amount of sodium hydroxide (pH adjuster), per 50 mL, and the emulsion type is an oil-in-water type.

Example 2

1.8 g of soybean-derived lecithin (manufactured by FUJIFILM Wako Pure Chemical Corporation) was dissolved in 200 mL (183 g) of soybean oil (RIKEN Nosan-Kako Co., Ltd.) (1% by mass of soybean-derived lecithin per 100% by mass of soybean oil), and the resulting solution was warmed in a thermostat bath at 60° C. 1000 mL of water was boiled, and 6.2 g of kanten was dissolved in the water (5 g of kanten per 800 mL of water). 800 mL of the water having dissolved kanten was collected while being filtered through a screen, and was cooled to 60° C. The soybean oil containing soybean-derived lecithin was then mixed in the water having dissolved kanten at a time, and the resulting mixture was then stirred with a blender. The obtained mixed liquid was transferred into a container, and stirred with a glass rod while being cooled with iced water, and was put in a refrigerator at the time when the liquid started setting, so that the liquid was solidified. In this way, a phantom of Example 2 (water:lipid=80:20 (volume ratio)) was obtained.

Example 3

3.7 g of soybean-derived lecithin (manufactured by FUJIFILM Wako Pure Chemical Corporation) was dissolved in 400 cc (368 g) of soybean oil (RIKEN Nosan-Kako Co., Ltd.) (1% by mass of soybean-derived lecithin per 100% by mass of soybean oil), and the resulting solution was warmed in a thermostat bath at 60° C. 600 mL of water was boiled, and 10 g of kanten was dissolved in the water (5 g of kanten per 300 mL of water), and the resulting solution was then cooled to 60° C. 300 mL of distilled water (no kanten) was mixed in the soybean containing soybean-derived lecithin at a time, and the resulting mixture was then stirred with a blender. In this mixture, 300 mL of the distilled water having dissolved kanten was mixed very little by little while stirring was performed with a glass rod. The obtained mixed liquid was transferred into a container, and stirred with a glass rod while being cooled with iced water, and was put in a refrigerator at the time when the liquid started setting, so that the liquid was solidified. In this way, a phantom of Example 3 (water:lipid=60:40 (volume ratio)) was obtained.

It was confirmed that the emulsion type of the mixed liquid obtained in the production method in each of Examples 2 and 3 was an oil-in-water type. That is, in a case where when an emulsion in which the volume ratio of water to the oil (water:oil) was 40:60 was made using an emulsifier, oil was mixed in water at a time as in Examples 2 and 3, an oil-in-water emulsion was obtained (FIG. 1A). On the other hand, in a case where water was mixed with (added to) the oil little by little, a water-in-oil emulsion was obtained (FIG. 1B). Soybean lecithin was used as the emulsifier, and soybean oil was used as the oil.

For evaluation of the phantoms of Examples 1 to 3, a six-wavelength time-resolved spectroscopy system (TRS-21-6W) and a magnetic resonance imaging method (MRI) were used.

<Measurement by TRS-21-6W>

(Apparatus)

FIG. 2A shows the appearance of an apparatus used for measurement by TRS-21-6W, and FIG. 2B shows a block diagram of the configuration of the apparatus.

The TRS system is composed of a light source, two photodetector units, a TRS circuit and an optical fiber (FIGS. 2A and 2B). The light source has six laser diodes (762 nm, 802 nm, 838 nm, 908 nm, 936 nm and 976 nm) each radiating a pulse laser beam having a pulse width of 100 ps to 200 ps (full width at half maximum), and a frequency with a pulse repetition rate of 5 MHz.

A subject was irradiated with a pulse laser beam through an optical fiber for a light source. Light propagated through the subject was collected at an optical fiber for detection, and guided to two photodetectors having different types of photomultiplier tubes (GaAs and InGaAs PMT, Hamamatsu Photonics K. K.). The detected light was converted into an electric signal by a photodetector unit, and processed in a TRS circuit designed on the basis of a time correlated single photon counting (TCSPC) method. The processed signal was acquired as a temporal profile of the detected light. In place of InGaAs PMT, MPPC (multi-pixel photon counter) can be used.

(Data analysis) In the TRS system, the measured temporal profile is analyzed on the basis of the light diffusion theory to measure the absorption coefficient (μ_(a)) and the reduced scattering coefficient (μ_(s)′) of a biotissue or the like in a scattering medium. The behavior of photons in the scattering medium is given by the photon diffusion equation (Appl. Opt. 28(12), 2331-2336 (1989)).

$\begin{matrix} {{{{\frac{1}{c}\frac{\partial}{\partial t}{\varphi \left( {r,t} \right)}} - {{\nabla{\cdot {D(r)}}}{\nabla{\varphi \left( {r,t} \right)}}} + {{\mu_{a}(r)}{\varphi \left( {r,t} \right)}}} = {S\left( {r,t} \right)}},} & (1) \end{matrix}$

Here, ϕ(r,t) represents a diffuse photon fluence rate at a position r and a time t, D=1/3 μs′ represents a photon diffusion coefficient, c represents a velocity of light in a medium, and S(r,t) represents a light source.

In the TRS system, temporal profiles measured in refection and transmission arrangements can be analyzed by using analytic solutions of the photon diffusion equation obtained under several types of boundary conditions. Here, the phantom was measured in a reflection arrangement at a-source-detector separation d. A diffusion reflectance R (d,t) obtained from a solution of the equation (1) for a semi-infinite homogeneous model having an extrapolated boundary condition is given by the following equation.

$\begin{matrix} {{{R\left( {d,t} \right)} = {\frac{1}{2}\left( {4\pi \; {Dc}} \right)^{{- 3}/2}t^{{- 5}/2}{{\exp\left( {{- \mu_{a}} {ct}} \right)} \cdot \left\lbrack {{z_{0}{\exp \left( {- \; \frac{z_{0}^{2} + d^{2}}{4\; {Dct}}} \right)}} + {\left( {z_{0} + {2z_{e}}} \right){\exp \left( {- \frac{\left( {z_{0} + {2z_{e}}} \right)^{2} + d^{2}}{4{Dct}}} \right)}}} \right\rbrack}}},} & (2) \end{matrix}$

Here, z₀=1/μ_(s)′ represents a transport mean free path, z_(e)=2D(1+r_(d))/(1−r_(d)) represents a linear extrapolation distance. r_(d) represents an internal reflectance associated with variance in reflectance at a boundary, and is calculated from an approximate equation dependent on the refractive index (n) of a medium (r_(d)=−1.440n⁻²+0.710n⁻¹+0.668+0.0636n). Therefore, the estimated temporal profile is obtained by calculating a convolution of an instrument response function (IRF) at R(d,t) in consideration of influences of IRF (J. Biomed. Opt. 1(3), 330-335 (1996), J. Biomed. Opt. 8 (3), 512-517 (2003)). μ_(a) and μ_(s)′ of a medium are determined by fitting the estimated profile to the measured profile by using a non-linear least-squares method based on the Levenberg-Marquardt algorithm. The absorption coefficient obtained for each wavelength λ is given by the following linear combination.

$\begin{matrix} {{{\mu_{a}(\lambda)} = {\sum\limits_{i = 1}^{m}{C_{i}{ɛ_{i}(\lambda)}}}},} & (3) \end{matrix}$

Here, m represents the number of light absorbing substances, C_(i) represents a concentration, and ε_(i)(λ) is an absorption coefficient of the ith light absorbing substance. The absorption coefficient can be measured by a spectrophotometer, and the concentration is determined by the simultaneous equations of the formula (3). Although main light absorbing substances absorbing light having a near infrared wavelength in a biotissue include deoxyhemoglobin, oxyhemoglobin, water and lipid, the light absorbing substances in the proposed phantom were assumed to include only water and lipid. Further, absorption of light by the emulsifier and the coagulating agent was assumed to be negligible. The absorption spectrum of water was measured by using a spectrophotometer (U-3500, Hitachi High-Technologies Corporation, Tokyo, Japan). The absorption spectrum of the lipid used is reported in a document (J. Biomed. Opt. 10(5), 054004 (2005)).

(Measurement by MRI)

Data was acquired by using a 3.0T MR unit (Discovery 750w, GE Healthcare, Waukesha, Wis.). As a proton density fat fraction (PDFF) pulse sequence, a commercially available sequence provided by a manufacturer of a MR unit (IDEAL IQ, GE Healthcare) (Radiology, 284(1), 244-254 (2017), Magn. Reson. Med. 77(4), 1516-1524 (2017)). The pulse sequence refers to a multipoint Dixon technique in which a T1 flip angle is used to limit a T1 bias, six echos for modifying a T2 effect, and a multipeak fat model is used. The parameters of this sequence are as follows.

Cycling time: 7.3 ms; minimum echo time: 3 ms; visual field: 40×40 cm; matrix: 160×160; band width: 111.1 kHz; flip angle: 4°; section thickness: 7 mm; one-dimensional image having 36 sections.

By using software provided by the manufacturer of the MR unit (IDEAL IQ, GE Healthcare), an image was processed to prepare water, lipid, R2* and lipid fraction maps. The phantom was redisposed in the reverse direction, data were then acquired twice, and two additional measurements were made. The lipid fraction of the phantom was measured by using a medical imaging system (SYNAPSE Version 4.1, Fujifilm Medical, Tokyo, Japan). The water fraction was determined by subtracting the lipid fraction from 100%.

<Evaluation>

The amounts of water and lipid in each phantom were measured by a six-wavelength TRS system and MRI, and the results were compared with theoretical values. A TRS system probe was installed at the center of the phantom. In the lipid fraction map obtained by MRI, a rectangular region of interest (ROD of 2 cm×5 cm was disposed immediately under the surface at the horizontal center of the phantom. For each phantom, an average value of four measured values was obtained.

FIG. 3 shows photographs of the upper surfaces, the cut sections and the MRI results of various phantoms. It was possible to easily cut out the phantoms of Examples 1 to 3 without losing their shapes. The phantoms of Examples 1 to 3 were homogeneous (see the photographs of cut sections in FIG. 3).

The amount of lipid in each of various phantoms was measured by MRI, and by using ImageJ/Fuji Software, the lipid amount distribution was evaluated over a range from the surface to the bottom surface of a 1 cm-wide ROI (region of interest) positioned at the center of the phantom (Nat. Methods, 9(7), 676-082 (2012)). The results are shown in FIG. 4. The results of lipid amount distributions in FIG. 4 showed that the phantoms were homogeneous.

FIG. 5A and FIG. 5B shows the results of measuring the optical properties (absorption coefficient and scattering coefficient) of various phantoms. FIG. 5A shows the results of measuring the absorption coefficients of various phantoms. The measured values at 935 nm and 975 nm were consistent with the peak absorption characteristics of lipid and water. FIG. 5B shows the scattering coefficients of various phantoms measured by TRS-21-6W. The phantoms of Examples 1 to 3 each had a scattering coefficient (5 to 15 cm⁻¹) close to that of a living organism (FIG. 5B).

FIG. 6A and FIG. 6B shows the results of measuring the amounts of water and lipid in each phantom by the six-wavelength TRS system and MRI. The results of measurement by the six-wavelength TRS system and MRI revealed that the measured values of the amounts of water and lipid were close to theoretical values, and phantoms having a desired water/lipid ratio were accurately made.

Next, the long-term stability of various phantoms was evaluated. The results are shown in FIGS. 7A, 7B and 7C. The long-term stability of the phantoms was evaluated by measuring the optical properties (absorption coefficient and scattering coefficient) of the phantoms every week by TRS-21-6W. As shown in FIG. 7A, FIG. 7B and FIG. 7C, the phantoms of Examples each maintained a scattering coefficient close to that of a living organism for at least a month. Further, it was not confirmed that the scattering coefficient significantly varied with time. Thus, the phantoms of Examples were shown to be excellent in long-term stability of optical properties (absorption coefficient and scattering coefficient). Further, the phantoms of Examples 1 to 3 each had a scattering coefficient close to that of a living organism even at the point of time when two months passed. 

What is claimed is:
 1. A phantom comprising: water, an oil; an emulsifier, and a water coagulating agent, and having a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm.
 2. The phantom according to claim 1, wherein the water coagulating agent is kanten.
 3. A method for producing a phantom, comprising: a mixing step of mixing water, an oil, an emulsifier and a water coagulating agent to obtain a mixed liquid, the phantom having a scattering coefficient of 5 to 20 cm⁻¹ at a wavelength of 750 to 1000 nm.
 4. The method for producing a phantom according to claim 3, wherein the mixing step comprises producing an oil-in-water emulsion by performing stirring under a condition in which at least a part of the water, the oil and the emulsifier are present.
 5. The method for producing a phantom according to claim 3, comprising a step of solidifying the mixed liquid.
 6. The method for producing a phantom according to claim 4, comprising a step of solidifying the mixed liquid. 